1. Field of the Invention
The present invention relates to a humidifying apparatus for a water permeable fuel cell that uses, for example, a hollow fiber membrane.
2. Description of the Related Art
A fuel cell mounted on a fuel cell vehicle has a structure wherein an electrode membrane structure providing an anode electrode and a cathode electrode on either side of a solid polymer electrolyte membrane is laminated on a separator that forms the gas passage for supplying various reaction gasses to both sides of this electrode membrane structure and at the same time supports the electrode membrane structure from both sides.
In this fuel cell, hydrogen gas is supplied to the anode electrode as a reaction gas for the fuel, and oxygen or air is supplied to the cathode electrode as a reaction gas for oxidation, and the chemical energy involved in the oxidation-repipeion reaction of these gases is extracted as direct electrical energy.
That is, at the anode electrode side the hydrogen gas is ionized and diffuses through a solid polymer electrolyte, and the electrons migrate to the cathode electrode side by passing through the external load, and the electrical energy can be extracted by a series of electrochemical reactions that generate water by reacting with oxygen.
However, in this fuel cell, when the solid polymer electrolyte membrane dries out, the ion conductivity decreases, leading to a decrease in the energy conversion efficiency Therefore, in order to maintain satisfactory ion conduction, moisture must be supplied to the solid polymer electrolyte membrane.
In order to attain this object, in this type of fuel cell, a humidifying apparatus is provided that supplies the reaction gas for the fuel and the reaction gas for the oxidizing agent after they have been humidified, supplies moisture to the solid polymer electrolyte membrane, and thereby maintains the satisfactory reaction.
A water permeable humidifying apparatus providing a hollow fiber membrane that permits the permeation of steam in the direction of the thickness of the membrane, such as that disclosed in Japanese Unexamined Patent Application, First Publication, No. Hei 8-273687, is known as a humidifying apparatus of this type.
FIG. 8 is a structural diagram of a fuel cell system providing the conventional humidifying apparatus. The air that is used as a reaction gas for the oxidizing agent is pressurized by the super charger 81, supplied to the humidifying apparatus 80A on the cathode electrode side via the pipe 82 for the reaction gas for the oxidizing agent, and supplied to the cathode electrode of the fuel cell 83 (below, referred to as the FC stack) after being moisturized in the humidifying apparatus 80A on the cathode electrode side. In addition, after the oxygen in the air supplied to the cathode electrode is used as the oxidizing agent, it is discharged from the FC stack 83 as off gas. The off gas that includes moisture generated during the reaction in the FC stack 83 is sent to the humidifying apparatus 80A on the cathode electrode side via the pipe 84 for the off gas from the FC stack 83, the steam in the off gas in the humidifying apparatus 80A on the cathode electrode side is taken up by the reaction gas for the oxidizing agent, and thereafter, is discharged.
In addition, the hydrogen gas used as the reaction gas for the fuel is supplied to the humidifying apparatus 80B on the anode electrode side via the gas pipe 85 for the fuel supply, is moisturized in the humidifying apparatus 80B on the anode electrode side, and then supplied to the anode electrode of the FC stack 83. In addition, a part of the oxygen supplied to the anode electrode is used as fuel and supplied to the oxidation-reduction reaction. After this one part of the oxygen gas has been supplied to the reaction, it becomes off gas and is discharged from the FC stack 83.
However, the solid polymer electrolyte membrane possesses the property that steam is caused to permeate from the side having a high moisture concentration to the side having a low concentration, where the solid polymer electrolyte membrane serves as a boundary, as a result of the ion hydration effect. As described above, the moisture concentration of the off gas flowing through the cathode electrode side is higher than that of the off gas flowing through the anode electrode side because it includes moisture generated during the reaction, but due to the ion hydration effect, the moisture in the off gas flowing through the cathode electrode side becomes steam, permeates the solid polymer electrolyte membrane, and diffuses into the off gas flowing through the anode electrode side. Therefore, moisture is included in the off gas on the anode electrode side.
The off gas on the anode electrode side that includes this moisture is sent to the humidifying apparatus 80B on the anode electrode side from the FC stack 83 via the off gas pipe 86, the steam in the off gas in the humidifying apparatus 80B on the anode electrode side is delivered to the reaction gas for the fuel, and subsequently, discharged.
Here, a humidifying module, which is the essential structural component of the humidifying apparatus 80A on the cathode electrode side and the humidifying apparatus 80B on the anode electrode side, will be explained referring to FIG. 7.
In the humidifying module 30, a plurality of bundled tube shaped porous hollow fiber membranes 32 comprising a steam permeable membrane (water permeable membrane) are accommodated, partition members 33 that bundle both ends of the hollow fiber membranes 32 are joined airtight to the outer surface of the hollow fiber membrane 32 or the inner surface of the hollow fiber membrane 32 and the outer peripheral surface of the housing 31. One end of the housing 31 communicates with the inlet head 34, and the other end communicates with the outlet head 35. In addition, gas inlet holes 36a and gas outlet holes 26b are provided more inward than both of the partition members 33, which are the peripheral part of the housing 31. The gas inlet holes 36a and gas outlet holes 36b communicate with an round internal passage of the round inlet cover 37a and the round outlet cover 37b that are respectively provided along the exterior peripheral surface of the housing 31.
In addition, in this humidifying module 30, the reaction gas is supplied to the round internal passage of the round inlet cover 37a, is introduced into the housing 31 from the gas inlet hole 36a, and flows in the round internal passage of the round outlet cover 37b from the outlet hole 36b after passing through the hollow fiber membrane 32 in the housing 31. In contrast, the off gas is supplied to the inlet head 34, enters into hollow part of the hollow fiber membrane 32 after being supplied to the housing 31 from the inlet head 34, and flows to the outlet head 35 from the other end of the housing 31 after passing through this hollow part. When the reaction gas and the off gas are caused to flow in this manner, the moisture in the off gas is taken up by the reaction gas via the hollow fiber membrane 32, and thereby, the reaction gas is humidified. Moreover, as one manner of using the humidifying module 30, the off gas can flow into the hollow part of the hollow fiber membranes 32, and the reaction gas can flow between the hollow fiber membranes 32, and in this manner as well, the moisture in the off gas can be taken up by the reaction gas via the hollow fiber membrane 32 to produce the humidifying.
In addition, the humidifying apparatus 80A on the cathode electrode side and the humidifying apparatus 80B on the anode electrode side can be provided with a plurality of humidifying modules 30, and in this case, the reaction gas supply pipes communicate with the inlet head 34 of each of the humidifying modules 30, the reaction gas discharge pipe communicates with the outlet head 35 of each of the humidifying modules 30, the off gas supply pipe communicates with the round outlet cover 37a of each of the humidifying modules, and the off gas discharge pipe communicates with the round outlet cover 37b of each of the humidifying modules 30.
Conventionally, the humidifying apparatus 80A on the cathode electrode side and the humidifying apparatus 80B on the anode electrode side are provided respectively as separate units, but there is the problem that the installation space becomes large. As a countermeasure for this problem, downsizing the installation space by combining both humidifying units 80A and 80B into one unit has been proposed.
In this case, generally all of the modules 30 for humidifying on the cathode electrode side and for humidifying on the anode electrode side are disposed so as to be parallel to each other in their longitudinal directions, and the ends of the inlet heads 34 and the outlet heads 35 of all of the humidifying modules 30 are disposed arranged on the same plane.
In the humidifying module 30, the four passages for the reaction gas supply, the reaction gas discharge, the off gas supply, and the off gas discharge must be connected, and in the case that the humidifying module 30 for the cathode electrode side and the humidifying module 30 for the anode electrode side are made into a unit, twice the number, or eight, passages must be connected in the unit.
However, as described above, when the end surfaces of the heads 34 and 35 of all the humidifying modules 30 are disposed so as to be aligned, and many of the paths among the eight paths are arranged on the same plane in the direction that is perpendicular to the longitudinal direction of the humidifying module on the outside end surface of the humidifying module 30, there are cases where the passages interfere with each other and cannot be easily arranged. Therefore, in the case that they cannot be easily arranged, the passages must be arranged so as to be shifted in the longitudinal direction of the humidifying module 30. However, when arranged in this manner, the length in the longitudinal direction of the humidifying module in the entire unit that includes the passages becomes long, and there is the problem that it cannot be formed compactly.
Thus, the present invention provides a humidifying apparatus for a fuel cell that allows the humidifying module for the cathode electrode side and the humidifying module for the anode electrode side to be formed compactly in one unit.
In order to resolve the above-described problems, the present invention provides a humidifying apparatus for a fuel cell (for example, the humidifying unit 20 in the embodiment described below) that provides a plurality of humidifying modules (for example, the humidifying modules 30A to 30E in the embodiment described below) that humidify the supplied gases by moisture being diffused between a reaction gas (for example, the air and hydrogen gas in the embodiment described below) supplied to the fuel cell for (for example, the FC stack 6 in the present embodiment described below) and the discharge gas (for example, the air off gas and the hydrogen off gas in the embodiment described below) discharged from the fuel cell and humidifies each of both electrodes of the fuel cell, wherein: all of the plurality of humidifying modules are disposed parallel to each other in their longitudinal direction, and at the same time, a portion of the humidifying modules among the plurality of humidifying modules (for example, the hydrogen humidifying module 30A in the embodiment described below) is disposed so as to shift their positions in the longitudinal direction from the other humidifying modules (for example, the hydrogen humidifying module 30B and he air humidifying modules 30C to 30E in the embodiment described below), and in the space formed by this shift (for example, the space S in the embodiment described below), a part of the path (for example, the air off gas discharge pipe 43 in the embodiment described below) that the reaction gas and the discharge gas pass through is perpendicular to the longitudinal direction and provided in proximity to the portion of humidifying modules.
Due to being structured in this manner, the length along the axial direction of the humidifying module in the humidifying apparatus for a fuel cell can be shortened.